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Frost blankets keep exotic plants cozy

By JANE WEBER
Published February 26, 2007


Last week's freeze zapped the leaves of many exotic palms and palmlike cycads. Particularly hard hit in Citrus County were queen palm, Syagrus romanzoffana, and Chinese fan palm, Livistona chinensis, both listed as invasive in South Florida. Fortunately, their seedlings are killed by freezes, so these popular plant pests do not naturalize this far north.

The cycads - king sago, Cycas revoluta, native to Japan; queen sago, Cycas rumphii, from tropical Pacific islands, and Mexican cardboard plant Zamia maritima, formerly Z. furfuracea - also suffered frost damage to their fernlike leaves. A long-term, hard freeze will kill them.

Covering these frost-tender exotic cycads is a must. Gardeners should use white, spun polypropylene crop cover fabric, dubbed "frost blanket," that can be purchased from most privately owned nurseries and growers.

If household sheets and quilts are used, they become wet with condensation and dew, ice up and stick to leaves and conduct heat away from the plant. Plastic tarps are worse. Because porous frost blankets breathe, heat buildup is eliminated and moisture passes through.

A frost blanket can be left in place for a month or more if the Florida gardener expects to be away during winter. It protects plants from insects, wind chill and cold by containing heat radiated from the earth. Ultraviolet-, rot- and mildew-resistant, it can be reused for years. Tears can be repaired with a stapler.

The blanket must be secured to the ground with some heavy material such as a piece of wood or bricks to work effectively.

Coonties tolerate freezing as they are native to Florida in zones 8 to 11. In the United States, coonties range from the northern parts of the Florida peninsula southward and are the same species that grow on Hispanola in the Caribbean Sea, where they were first discovered.

There are several geographic populations having slightly different characteristic leaf sizes, which formerly led to a variety of species names. Botanists and nursery operators now call coonties by the original scientific binomial Zamia plumila given them by Linnaeus centuries ago.

Swedish naturalist Carl von Linne, Carolus Linnaeus (1707-78) even "Latinized" his own name.

Coontie, in the Zamiaceae family, predates the dinosaurs and is the only cycad now existing naturally in our country. It has a fattened, turniplike, underground stem that contains a starch once used for subsistence.

Factories processed the starch until 1925, when the slow-growing plant was virtually eradicated in the wild. All cycads contain dangerous cycasin that must be thoroughly washed out before human consumption. Long-term brain damage can result from eating cycasins. Read neurologist Oliver Sacks' Island of the Cycads for fascinating information.

The state placed coonties on a protective list that bans harvesting plants or parts, including seeds, from the wild. Fortunately, licensed growers have helped the species recover so nursery-grown plants are readily available.

Of about 20,000 coonties in my garden, only 5 percent will mature as females to produce seed. I wholesale coonties at $1.25 for each year of growth. An 8-year-old, with up to a dozen leaves sprouting from one crown, wholesales for about $10. Retailers with higher overheads must charge about $20.

To avoid frost damage in the future, buy some proper frost blanket now. If covering tender exotics is not your cup of tea on a blustery, frigid afternoon, then replant your damaged cycads in sandy, well-drained soil in large patio pots that can be brought indoors.

Heat radiating from a pool may keep frost from settling on nearby plants. Potted plants will bonsai and not grow much bigger as their root growth will be restricted.

Fill the garden with hardy, low-maintenance coonties and native palms. More about coonties next week.

Editor's note: This weekly article is provided by Jane Weber, professional gardener, grower, consultant, designer and environmentalist. Visit her Certified Florida Yard and Backyard Wildlife Habitat, 5019 W Stargazer Lane, Dunnellon. Call (352) 465-0649.